1. Field of the Invention
The present invention relates to a Schottky barrier diode and a method of fabricating Schottky barrier diodes, and more particularly to a Schottky barrier diode that utilizes heterojunction bipolar transistor (HBT) active device layers to provide a Schottky barrier diode with reduced resistance between its barrier and ohmic contacts, which results in relatively high performance and high reliability and enables the Schottky barrier diode to be relatively easily integrated with other GaAs integrated circuits to form monolithic multifunction integrated circuits.
2. Description of the Prior Art
Schottky barrier diodes are generally known in the art. Such diodes are generally used in applications, such as high-frequency sample-and-hold amplifiers and analog-to-digital converters. Schottky barrier diodes are also used in various microwave and millimeter wave applications.
Schottky barrier diodes are known to be made from various processes. For example, some known Schottky barrier diodes are fabricated from silicon processes. Schottky barrier diodes formed from silicon processes are known to have relatively poor performance due to minority carrier injection from the lower silicon Schottky barrier. Silicon processing is also known to yield-Schottky barrier diodes with relatively high-parasitic capacitances. As such, Schottky barrier diodes fabricated from silicon are known to provide poor performance in some applications, while unsuitable for other applications.
Schottky barrier diodes are also known to be formed from heterojunction bipolar transistor (HBT) processing techniques, which utilize a GaAs substrate. An example of an HBT process for fabricating a Schottky barrier diode is disclosed in copending application Ser. No. 08/556,321, filed on Nov. 8, 1995, entitled "METHOD OF FABRICATING MONOLITHIC MULTIFUNCTION INTEGRATED CIRCUIT DEVICES", by C. Streit, D. K. Umemoto, A. K. Oki and K. Kobayashi, assigned to the same assignee as the present invention and hereby incorporated by reference. In that application, an n+ subcollector layer is epitaxially grown on a GaAs substrate. An n- collector layer is subsequently epitaxially grown on top of the subcollector layer and etched to form a collector mesa. A barrier contact is formed on top of the collector mesa, while an ohmic contact is formed on the subcollector layer, adjacent the collector mesa.
In the above-mentioned copending application, the Schottky barrier diode is integrated onto the same wafer with an HBT. As such, the subcollector layer of the Schottky barrier diode is formed with generally the same thickness as the subcollector layer of the HBT. As such, the current path and thus the series resistance between the barrier and ohmic contacts is relatively high, resulting in lower-than-desired cut-off frequency performance.